1. Field of the Invention
The invention relates to broadside small array microphone beamforming unit, and in particular to low noise adjustable beams for broadside small array microphone beamforming unit.
2. Description of the Related Art
Many communication system and voice recognition devices are designed for use in noisy environments. Examples of such applications include communication and/or voice recognition in cars or mobile environments (e.g., on street). For these applications, the microphones in the system pick up not only the desired voice but also noise as well. The noise can degrade the quality of voice communication and speech recognition performance if it is not dealt with in an effective manner.
Noise suppression is often required in many communication systems and voice recognition devices to suppress noise to improve communication quality and voice recognition performance. Noise suppression may be achieved using various techniques, which may be classified as single microphone techniques and array microphone techniques.
Single microphone noise reduction techniques typically use spectral subtraction to reduce the amount of noise in a noisy speech signal. With spectral subtraction based techniques, the power spectrum of the noise is estimated and then subtracted from the power spectrum of the noisy speech signal. The phase of the resultant enhanced speech signal is maintained equal to the phase of the noisy speech signal so that the speech signal is minimally distorted. The spectral subtraction based techniques are effective in reducing stationary noise but are not very effective in reducing non-stationary noise. Moreover, even for stationary noise reduction, these techniques can cause distortion in the speech signal at low signal-to-noise ratio (SNR).
Array microphone noise reduction technique use multiple microphones that are placed at different locations and are separated from each other by some minimum distance to form a beam. Conventionally, the beam is used to pick up speech that is then used to reduce the amount of noise picked speech that is then used to reduce the amount of noise picked up outside of the beam. Thus, the array microphone techniques can suppress non-stationary noise. Multiple microphones, however, also create more noise due to the number of microphones.
Thus, effective suppression of noise in communication system and voice recognition devices is desirable.